The prosecution of more than 300 journalists who used investigators to obtain private phone and address records and other personal information did not occur because it would not have been good regulation, the information commissioner told MPs today.

Christopher Graham, the information commissioner, said he and his predecessor in the role office, Richard Thomas, did not have the resources to investigate all the journalists that the Motorman inquiry discovered had used private investigators to illegally obtain personal information.

"It would not have been good regulation for the information commissioner's office to prioritise this particular bit of the jungle. We are concerned with the whole trade in information," Graham said today, at a hearing of the Commons culture, media and sport select committee's inquiry into press standards, privacy and libel.

Graham, who took over from previous information commissioner Thomas in June, was answering questions arising from the Motorman inquiry into investigator Steve Whittamore, which turned 17,500 information requests from 305 journalists.

Instead the commissioner's office took a deterrent option, with its two reports to parliament and its warning that illegally obtaining information not in the public interest was punishable by imprisonment.

Graham also criticised newspapers because none of the journalists or newspapers named in the 2006 information commissioner's report, What Price Privacy Now, responded seeking further information.

The information commissioner rejected the committee's contention that it had not acted appropriately. "It was the information commission's office who highlighted the whole thing. We are the good guys in all this," Graham said.

On Monday, the Guardian revealed scores of names of politicians, celebrities and other figures that the information commissioner uncovered during the Motorman inquiry, including Joanna Lumley and the Private Eye editor Ian Hislop.

This followed earlier stories by the Guardian alleging that the practise of phone hacking by News of the World journalists had been more widespread than the paper had previously admitted.

"I don't what to get into a battle between two newspaper groups," Graham said.

He added that he was disappointed in the reaction to the information commissioner's report What Price Privacy Now, which recommended imprisonment for the illegal gathering of information held by BT and the DVLA.

""Any fines you get from magistrates can be written off as a business expense … We were let down by the courts, who didn't seem to be interested in levying even the pathetic fines they had at their disposal; we were rather let down by parliament in the end, with no legislation; and we were let done by the newspaper groups, which didn't take it seriously," he said.

To pursue the journalists to the detriment of the office's other activities would have been "irresponsible given everything else that parliament has charged the information commissioner to deal with".

He described the scale of the illegal accessing of personal information as "an appalling situation", but said it would have been impractical for his predecessor, to pursue action against every journalist featured in the report, given that there were more than 17,000 invoices or purchase orders.

"You would have to go through [each individual case] forensically to achieve the standard of proof required in a court of law, attach each to a story … and work out if our lawyers could get the better of their [newspaper] lawyers," Graham added. "The appropriate response was to make big issue of it … tackling it at source and at the top level by legislation."

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